ISSUE-20167: [Doc] Message retention detail explanation

[sijie]

Original Issue: apache#20167

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• I searched in the issues and found nothing similar.

What issue do you find in Pulsar docs?

The retention in the detailed explanation makes me feel confused. I don't know if this means Always resolved message or Always delete message. If I understand it with Disable the message retention policy which means the messages will never be deleted.

What is your suggestion?

Let's change it to Disable message retention, which means messages are not reserved (by default).

Any reference?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!